1. Field of the Invention
The present invention relates to an liquid-jet recording head and an liquid-jet recording apparatus, in which part of a pressure generating chamber to communicate with a nozzle orifice for ejecting liquid droplets is composed of a vibration plate and a piezoelectric element is formed on a surface of this vibration plate so as to cause ejecting of liquid droplets by displacement of the piezoelectric element. More particularly, the present invention relates to an ink-jet recording head that ejects ink as the liquid and to an ink-jet recording apparatus.
2. Description of the Prior Art
An ink-jet recording head, in which part of a pressure generating chamber to communicate with a nozzle orifice for ejecting ink droplets is composed of a vibration plate so as to cause ejecting of ink droplets out of the nozzle orifice by displacing this vibration plate with a piezoelectric element and thereby pressurizing the ink in the pressure generating chamber, has two types that are already in practical use, namely, one using a piezoelectric actuator of a longitudinal vibration mode which expands and contracts in an axial direction of a piezoelectric element, and one using a piezoelectric actuator of a flexure vibration mode.
The former one enables fabrication of a head suitable for high-density printing because the volume of the pressure generating chamber is made variable by allowing an end surface of the piezoelectric element to abut on a vibration plate. On the other hand, the former one has a problem that the fabrication process becomes complicated since a difficult process of carving the piezoelectric elements into comb-teeth shapes so as to be aligned with an arrangement pitch of the nozzle orifices, and an operation of positioning and fixing the carved piezoelectric elements onto the pressure generating chambers are required.
On the contrary, the latter one enables formation of the piezoelectric elements on the vibration plates by a relatively simple process of attaching a green sheet made of a piezoelectric material so as to agree with the shapes of the pressure generating chambers and then by baking the green sheet. However, the latter one has a problem that a high-density arrangement becomes difficult because a certain degree of area is required to utilize flexure vibration therein.
Meanwhile, in order to solve the inconvenience of the latter recording head, there is proposed a technology in which a uniform piezoelectric layer is formed over the entire surface of the vibration plate by use of a film-forming technology and this piezoelectric layer is carved into shapes corresponding to pressure generating chambers by a lithography method to form piezoelectric elements individually for the respective pressure generating chambers (refer to, for example, Japanese Patent Laid-Open No. 5(1993)-286131).
According to this technology, an operation of attaching piezoelectric elements to a vibration plate becomes unnecessary. Therefore, the technology provides not only a capability of forming the piezoelectric elements in high density by use of the accurate yet simple technique called the lithography method, but also provides an advantage that high-speed driving can be achieved by virtue of reducing the thickness of the piezoelectric element.
However, in such an ink-jet recording head having piezoelectric elements arranged in high density, one of electrodes (a common electrode) of each piezoelectric element is provided in common to a plurality of piezoelectric elements. Accordingly, if many piezoelectric elements are driven simultaneously to eject many ink droplets at one time, there occurs a problem that a voltage drop arises and the amount of displacement of the piezoelectric elements becomes unstable, whereby an ink ejecting characteristic is deteriorated.
Such a problem may be solved by increasing the thickness of the common electrode of the piezoelectric elements. However, since this common electrode includes part of the vibration plate, the amount of displacement of the vibration plate drops due to the drive of the piezoelectric elements. Alternatively, this problem may be solved by increasing the area of the common electrode. However, the size of the head is increased in this case.
Moreover, the electrodes of the piezoelectric elements formed of thin films have relatively high resistance values because of the films are thin. Therefore, the problems as stated above are very likely to occur.
Note that such a problem as described above needless to say occurs in other liquid-jet heads ejecting liquids other than ink, similarly to the ink-jet recording head ejecting ink.